For example, any folder that's not special. You need to import all folders you created manually in em Client. However, you need to import the mbx files in a certain order. In the case of Sent.mbx, you're also going to set Sent.mbx in the "move to sent" drop-down. Once you pick the mbx file to import, you need to set "import into" to the existing POP account you already created. You're going to do this multiple times, one for each mbx file in the "converted folder. Now, what you need to do is go to "Menu -> Settings -> import and export -> import mail -> import generic mbox -> add mbox". Then, you're going to select all messages in "All Messages/Unread" and drag them to "FromServer" (just for now). Then, on the "options" tab, check "hide these messages from other views" and close out of the dialog. Right-click on "New Label" in the Labels access point and goto "properties". Right-click in the new mail panel and choose "New Label".
Now, in Opera Mail, choose to create a new POP account with the correct settings and let it download any messages on the server. When you're all done, the "converted" folder will have an mbx file for each folder. You then repeat for other folders you exported (change "Inbox" to "Name of folder"). The mbx file will contain all the messages in the Inbox. That will create an Inbox.mbx file in a folder named "converted" in the directory. Then, you're going to type a command and press enter. you can type dir and press enter to check that you see eml2mbx.exe etc. That will put in you in the correct folder.
In the command prompt, type this command: cd "yourusername" is your user name for Windows) Type cmd and press enter to launch a command prompt.
Then, you're going to hit the windows key on the keyboard and the r key at the same time to launch the run dialog. Then, you're going to select all files in it, cut and paste them into where you see all the exported folders. You're then going to extract eml2m065 to a folder. What you're going to do is download eml2mbx from. So, what you do is export all your folders to "C:\Users\yourusername\mymessages" using "File -> Export", which will give you folders of. If you're using IMAP, you just set up the IMAP account in Opera and you're done).
(Only do the following if you're using POP. Also, in "Menu -> File > export", you can choose to export whole folders of messages at once. That will allow you to save the selected messages as. However, you can select multiple messages in a list in eM Client, right-click the selectioin and choose "save as". I think you'd need a custom program that loads the database dat files, analyzes them and then converts them to mbox files (what Opera supports). Ok, eM Client uses SQLite databases (dat files in this case) for storage of everything (including messages).